1. Field of the Invention
The present invention relates to a memory control apparatus.
2. Description of the Related Art
In these years, a processor is mounted on many electronic devices. For example, Japanese Patent Laid-Open Publication No. 2006-253780 discloses an audio system in which a DSP (Digital Signal Processor) is mounted in addition to a radio tuner. In this audio system, a speech signal extracted by the radio tuner is subjected to digital signal processing in the DSP, and then is output as voice.
Also, electronic devices incorporating computer systems called built-in systems or embedded systems have been widespread. In such an electronic device, a CPU (Central Processing Unit) which is configured as a microprocessor is mounted, and the CPU executes various numerical calculations, information processing, device control, and the like according to programs.
The electronic device provided with a processor can flexibly support change to a specification by changing software even after design of hardware is completed. Therefore, products in accordance with customer needs can be supplied at appropriate timing. Further, even after the product is shipped, addition of a function in accordance with customer needs can easily be realized by change of software.
Here, an example of a general connection relationship between the processor mounted on the electronic device as above and memory is illustrated in FIG. 26. In FIG. 26, memory 3 to 5 is connected to a CPU 8, which is a processor. Also, similarly to FIG. 2 in Japanese Patent Laid-Open Publication No. 2006-253780, Harvard architecture with separate program memory and data memory is employed, and the memory 3 is used as the program memory, while the memory 4 and 5 are used as data memory #1 and data memory #2, respectively.
In such a configuration, if the design of the software is completed after the design of the hardware, as illustrated in FIG. 26, for example, a portion of each of the memory might result in an unused area. Also, even if the unused area of the memory can be minimized before shipment of the product, it might be desirable to leave the unused area so that a function can be added after the shipment of the product.
However, if the unused area remains in the memory, it is required to use memory with a capacity larger than the requisite minimum capacity. Thus, current consumption of each memory may be increased.